Having tried all three, its a stark difference in how much more social Lemmy is comparatively. Its not even close. Almost all posts I've encountered on lemmy have interaction; whereas, more often than not, posts on the other two platforms have no interaction. Wonder what the driving factor is behind this difference?
Twitter have big interaction because user count is extremely high. For a microblogging platform maybe it requires that it needs lots of users and some "creators" who are followed by thousands of people, unlike communities which anyone can post and everyone joined the community can see.
I also think upvotes and downvotes plays a role too since mastodon does not have them(only boosts but boost actually shares with your own followers which might be very low)